In recent years, as a fan motor for an air conditioner, a brushless motor has been mainstream to achieve high efficiency. A brushless motor has often employed a method in which a motor is driven by an inverter using a pulse width modulation system (to be arbitrarily referred to as a PWM system hereinafter). In the inverter driving of the PWM system, since the motor is driven by a drive signal of a high-frequency pulse, the drive signal may work as noise to cause electromagnetic interference in an external device. In a general electric apparatus, noise generated in a power supply and flowing into a power supply system of a circuit of another device through an output from the power supply is called a noise terminal voltage. Since the noise terminal voltage serves as a noise source, the noise terminal voltage causes electromagnetic interference to adversely affect a peripheral device.
For example, in an air conditioner, a noise terminal voltage generated from a motor built-in the air conditioner may considerably influence a level of a noise terminal voltage of the main body of the air conditioner. More specifically, in this case, the noise terminal voltage generated from the motor of the air conditioner may sneak into a power supply of another device through an air conditioner power supply and a commercial power supply system to cause electromagnetic interference.
As a method of reducing a noise terminal voltage, various methods such as a method of taking a measure on the air conditioner body side and a method of taking a measure on a fan motor side are known. As the method of taking a measure on the air conditioner body side, a method of enhancing a noise filter of a power supply line, a method of installing a capacitor (bypass capacitor) between the motor and the ground, and the like are known. As the method of taking a measure on a fan motor side, a method of attaching a ferrite core to a lead wiring, a method of adjusting a capacitance of a capacitor of a power supply line, and the like are used. The methods has been generally executed from long ago, and are common knowledge.
In the circumstances, a technique that improves a structure a motor to prevent noise from radiating from the motor is known. As an example of the technique, in a conventional molded motor in which a stator is molded with a resin, a technique that fixes bearings that support a motor shaft by two metal brackets, elastically couples the brackets with each other by a metal spring member, and makes the potentials of the brackets equal to each other to prevent noise from radiating from the motor and to reduce a noise terminal voltage is proposed (for example, see Patent Document 1).
However, the conventional method in Patent Document 1 has the configuration in which the brackets are coupled with each other by the metal spring member on an outer frame of the motor. For this reason, the spring member is easily influenced by external water, dust, impact, or the like, and has a problem in terms of durability. Since the spring member serving as a motor structure also functions to give breaking strength to a bracket, the spring member needs to be strong. For this reason, the spring member is expensive because the spring member is thick and large to pose a problem with cost.    Patent Document 1: Unexamined Japanese Utility Model Publication No. 1987-159143